i915: Map sampler indices to texture units correctly for fragment shaders.
i915: Map sampler indices to texture units correctly for fragment shaders.

Fixes hang with "gst-launch-0.10 videotestsrc ! video/x-raw-rgb !
glupload !  gleffects effect=heat ! glimagesink" which uses 2 samplers
pointing at GL_TEXTURE1 and GL_TEXTURE2, and piglit
glsl-fs-sampler-numbering.

zz85/glsl-optimizer,mcanthony/glsl-optimizer,KTXSoftware/glsl2agal,zz85/glsl-optimizer,metora/MesaGLSLCompiler,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,adobe/glsl2agal,dellis1972/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,metora/MesaGLSLCompiler,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,adobe/glsl2agal,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,adobe/glsl2agal,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,tokyovigilante/glsl-optimizer,KTXSoftware/glsl2agal,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,zeux/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer